Coupling Algorithm Research Articles

Investigation of casing stress distribution and parameter optimization during the transient impact process of multi-hole perforation operations

Perforation operation is critical in bridging completion and production enhancement operations. At the same time, the perforation parameters also affect the structural integrity of the casing. Still, there are fewer studies on the stress distribution of the casing under the blast transient impact loading of multi-hole perforation. To address this, considering the engineering application of helical perforation in unconventional oil and gas reservoirs, a three-dimensional numerical model of perforating charge-casing-cement sheath-formation is established, and the Holmquist-Johnson-Cook (HJC) rock dynamics material model, as well as the fluid–solid coupling and Arbitrary Lagrange-Euler (ALE) algorithms. On this basis, the variation rule and distribution characteristics of the effective stress in the double-perforation holes stress superposition area under different perforation density, phase angle, and geostress conditions are analyzed with the casing strength safety threshold as the optimization judgment condition of perforation parameters. The research results show that the numerical simulation result has good consistency in the results of engineering practice, perforation aperture diameter error is 3.04%, and jet head velocity error is 6.85%. The variation rule of perforation density and phase angle has a significant effect on the effective stress distribution in the stress superposition area around the hole: with the decreasing perforation density or increasing phase angle, the casing stress superposition area in the middle part of the neighboring perforation holes is gradually narrowed down, and when the perforation density is more than 9 P/m and 51°, the casing stress in the stress superposition area between the perforated holes is lower than the safety threshold value. With the increasing ground stress, the stress in the middle of the neighboring perforated holes increases continuously, showing a quadratic function change trend. The perforation density should be appropriately reduced, and the phase angle should be increased when the geostress is high to ensure the integrity of the casing structure after the perforation operation. The research results can provide a practical reference for conducting perforation engineering operations and optimizing perforation parameters.

On the concrete breakage by pulsed water jet impact: Fracture characteristic, stress and damage evolution laws

To reveal the dynamic response characteristic and damage-fracture evolution laws of concrete under pulse water jet impact, the numerical simulations on pulse water jets impinging concrete for different operating parameters were established based on SPH-FEM coupling algorithm and verified in this paper. The concrete-breaking effects of pulse water jet and continuous water jet were compared, and the effects of key jet parameters and concrete strength on the damage-fracture characteristics of concrete were investigated. And the damage and stress evolution laws inner concrete were revealed. The results show that there is a better concrete-breaking effect for pulse water jet by repeatedly utilizing the extremely high water-hammer pressure and effectively weakening the water-cushion effect, compared with continuous water jet. The broken pit area and the total length of main cracks decrease with the increase of pulse length, and there is an optimal pulse spacing for pulse water jet to improve the concrete-breaking effect. The broken pit area and the total length of main cracks both linearly increase with the increasing jet velocity and exponentially increase with the increasing jet diameter. As the concrete strength increases, the broken pit area shows an S-shaped curve decreasing trend and the total length of main cracks exponentially decreases. The broken pit width first rapidly increases and tends to stabilize with the increase of jet velocity and concrete strength, and changes linearly with jet diameter and is less affected by pulse length and spacing. The farther away from the jet impact center, the longer the damage cumulative period of concrete due to the jet impact energy attenuation. In horizontal direction, concrete breakage range is approximately 4–5 times of jet diameter; in vertical direction, the previous pulses will cause concrete to be destroyed or damaged, and the subsequent pulses will make the damaged concrete suffer greater stress, causing more serve damage. And the induced stress peak decreases in form of Power function with the increasing distance. The research results could provide theoretical guidance for the parameters selection of pulse water jet efficiently breaking concrete.

The thermal-fluid-mechanical (TFM) coupling method based on discrete element method (DEM) and the application of CO2 fracturing analysis

Due to the challenges of the complex temperature, fluid and mechanical coupling phenomenon during CO2 fracturing, a new thermal-fluid-mechanical (TFM) coupling method is proposed by using PFC2D fish code. This method utilizes the PFC2D fish code and combines the heat transfer difference algorithm with Cundall's fluid-mechanical coupling algorithm to establish a TFM model for CO2 fracturing. Subsequently, the validation of the TFM coupling model is conducted using the analytical solution provided by the plane strain Khristianovic Geertsma-de Klerk (KGD) model. The reservoir temperature variation, pore pressure and crack propagation are studied considering many involved factors, such as injection fluid temperature, injection flow rate, in-situ stress and formation temperature. Crack number and length would increase with the increasing temperature difference between fracturing CO2 and reservoir temperature. The breakdown pressure reduces when there are large injection flow rate or temperature differences between fracturing CO2 and reservoir temperature, which can be optimized in the CO2 fracturing operation. Even CO2 fracturing could create complex fracture network, we must pay attention to the in-situ stress distribution and injection flow rate. Our simulation suggests that pore pressure and heat could prevent the fracture from initiating and propagating in the direction of the minimum principal stress, and the temperature influencing has contributed to the extra pressure increment in the pore domain, which could not be ignored in CO2 fracturing. From the above research, it is expected to offer a novel method to simulate the complex TFM coupling phenomenon and enhance our understanding of CO2 fracturing.

$${\mathrm{H}}_{\infty }$$ and $${\mathrm{H}}_{2}$$ Optimization of the Grounded-Type DVA Attached to Damped Primary System Based on Generalized Fixed-Point Theory Coupled Optimization Algorithm

$${\mathrm{H}}_{\infty }$$ and $${\mathrm{H}}_{2}$$ Optimization of the Grounded-Type DVA Attached to Damped Primary System Based on Generalized Fixed-Point Theory Coupled Optimization Algorithm

An optimized DEM‐SPH model for surge waves induced by riverside landslides

AbstractRiverside landslides can induce surge waves during the process of entering water. The landslide‐induced surge wave is often regarded as a significant secondary disaster, as its impact region is likely to be even more remarkable than the landslide itself. Due to the large deformation of the soil landslide and water body during the evolution of surge waves, commonly adopted multi‐phase flow models and mesh‐based methods coupled with discrete element models have some limitations, such as weak accuracy, and simulation distortion with immature coupling algorithms. As a result, the pure meshless method of smoothed particle hydrodynamics (SPH) coupling discrete element methods (DEM) become promising. Modified from the traditional empirical formulae‐based coupling algorithm, this study proposes a semi‐resolved algorithm that effectively eliminates the particle distortion at the fluid‐solid coupling interface. The proposed model demonstrates its superiority through a comparison of the pressure and porosity near the coupling interface. Furthermore, the optimized DEM‐SPH model is applied to simulate landslide‐induced surge waves, and the simulation results have also validated the accuracy of the model. This model is capable of accurately simulating the entire propagation process from landslide entry into water to the wave reaching the opposite shore, and therefore provides an effective tool for the prediction and mitigation of wave hazards caused by landslides.

Interactive coupling of structural dynamics and milling forces for high-frequency stability prediction in robotic milling

Robotic machining has developed rapidly and has great potential for manufacturing large parts with complex surfaces. However, the machining quality and efficiency are severely limited by the low stiffness of the robots, which causes destructive chatter during manufacturing. To suppress this phenomenon, offline stability prediction must be performed before the actual robotic milling. In this study, a high-frequency stability prediction algorithm for robotic milling was developed by introducing an interactive method. A lightweight structural dynamic model of a robot was developed based on specially designed decoupling criteria, and an interpolation algorithm that determines the trajectory of the tool nose was designed to calculate the milling force. By combining the two models, an interactive coupling algorithm was proposed to forecast the vibration in robotic milling. The predicted results can contribute to generating the stability lobe, thereby verifying the stability distribution and spectral characteristics of both the simulated and measured signals. The new algorithm realizes static data communication and dynamic state updating between the dynamic and cutting force models at high frequencies, thereby balancing the simulation speed and prediction quality.

Verification of 3D DDA-SPH coupling method and its application in the analysis of geological disasters

At present, discontinuous deformation analysis (DDA) is in an active development stage and its application in the field of geohazards is expanding. Recently, the DDA method has been coupled with smooth particle hydrodynamics (SPH) to analyze some geohazards involving fluid-solid interactions (FSI) and has shown good prospects in the field. However, the interaction between rocks and water in geological disasters is extremely complex and the comprehensive verifications of the simulation results between the block and fluid under different interactive modes are never found. To solve this problem, we first introduced the basic principle of the DDA and SPH method, followed by the coupling algorithm of the two methods. Then, the correctness of the coupling method was verified through analyses of fluid and solid movement by adopting the dam break test, Scott Russell's wave generator experiment, water entry test of a single sphere, and landslide-generated impulsive wave, which represent different interaction modes between blocks and fluids respectively. Finally, based on the 3D DDA-SPH method, this paper simulated the chain disasters of the water inrush induced by tunnel collapse and the dam instability induced by slope sliding, and analyzed the chain mechanism between the different disasters, which illustrates the feasibility of 3D DDA-SPH coupling method in simulating the FSI problem in geotechnical engineering.

A coupling algorithm of ordinary and non-ordinary state-based peridynamic models for fracture analysis in brittle and ductile materials

In this work, a novel coupling algorithm of the ordinary state-based peridynamic (OSB-PD) model and non-ordinary state-based peridynamic (NOSB-PD) model is provided under the peridynamic framework. The salient advantages of both OSB-PD and NOSB-PD models can be simultaneously inherited in this coupling model and approach. The feasibility of coupling these two models is first analyzed by demonstrating the numerical equivalence of their constitutive formulations in isotropic elastic and elastoplastic problems, and the detailed numerical implementation strategy of coupling formulation is given as well. With the coupling model in this study, the main calculation procedure of numerical simulations is accomplished in OSB-PD, while the damage and failure analysis is conducted in NOSB-PD. Moreover, different failure criteria are introduced in this coupling model to describe the damage and failure of brittle and metallic materials. Several typical examples, including the mode I and mixed mode I/II fracture of brittle materials, and the ductile fracture and impact failure of metallic materials, are conducted to demonstrate the robustness and accuracy of the presented coupling model and approach.

Multi-parameter optimization of ferrofluid seal pole teeth based on magnetic-flow coupling and taboo genetic algorithm

Ferrofluid seals are a high-performance seal technology. Rational pole tooth structure and size can enhance the performance of ferrofluid seals. However, most current methods for optimizing pole tooth structure and size ignore the influence of the flow field. Therefore, this paper presents a pole tooth optimization method based on magnetic-flow coupling and considers the shaft rotational speeds. Combining this method with the taboo genetic algorithm establishes the mathematical model and simulation model of magnetic pole tooth size optimization. The optimal pole tooth size at different rotational speeds is obtained through optimization. Additionally, the effects of rotational speed and pole tooth parameters on pressure capacity are studied. The results show that both the rotational speeds and the parameters of the pole teeth significantly affect pressure capacity. The rotational speeds also influence the parameters of the pole teeth.

Research on neutron diffusion equation and nuclear thermal coupling method based on gradient updating finite volume method

To solve the problem that the neutron diffusion equation has infinite solutions when the deterministic method is used to calculate the neutron diffusion equation, this paper uses the power calculation equation as a supplementary equation to form a differential and integral equation groups with the neutron diffusion equation, and designs a numerical analysis and machine learning coupling algorithm based on the gradient updating finite volume method that can be used to solve the above differential and integral equation groups. The algorithm decouples the multigroup neutron diffusion equations by source iteration. Then the finite volume method is used to solve the one group neutron diffusion equation and the reactor core power. Based on the power difference calculated by two adjacent iterations, the neutron flux density is updated by the gradient descent method until it converges. Finally, the algorithm can be used to calculate the neutron flux density and volumetric heat release rate of each energy group under the specified power. Taking 5 × 5 rod bundle channel as an example, the feasibility of the algorithm is verified in Fluent 18.0 by writing the UDF script. In addition, the thermal–hydraulic parameters such as temperature and velocity in the reactor can be further calculated according to the volumetric heat release rate, and a same set of grids can also be used to achieve the nuclear thermal coupling calculation. This algorithm can provide a new calculation method for the neutron diffusion equation, and also provide a theoretical basis for the development of application algorithms in the field of reactor physics using deep learning.

Experimental research and finite element analysis on blast resistance of RRACFST columns

In order to research the dynamic response of rectangular recycled aggregate concrete-filled steel tubular (RRACFST) columns under blast loads, three contact blast experiments were carried out on three column models, and their different failure modes, dynamic strain rates and acceleration rates were determined. The numerical model was established using the arbitrary Lagrangian-Eulerian method and the fluid–solid coupling algorithm available in the explicit nonlinear finite element software LS-DYNA™, and the reliability and validity of the numerical model were verified by the experimental results. On this basis, the numerical model was used to analyze the parameters, as well as the effects of the replacement rate of recycled aggregate, column height, steel tube thickness and steel strength on the contact explosion resistance of RRACFST columns. Also, the advantages and disadvantages of overall refinement and local refinement are compared. The study results show that the RRACFST columns had basically no overall response to the action of contact blast loads, producing only a small explosion crater in the detonation area, without breaking the steel tube, and with no recycled aggregate concrete (RAC) overflows. The steel tube thickness was the decisive factor affecting the blast resistance performance of the RRACFST columns. In addition, for the numerical simulation of contact explosion, the local refinement was better than the overall refinement.

An iterative decomposition coupling algorithm between TD-FEM and TD-BEM with independent spatial discretization on the interface

An iterative decomposition coupling algorithm between TD-FEM and TD-BEM with independent spatial discretization on the interface

SmartSBD: Smart shared bottleneck detection for efficient multipath congestion control over heterogeneous networks

Multipath TCP (MPTCP) has been widely adopted in today’s mobile devices. However, two types of congestion control algorithms, uncoupled congestion control (Uncoupled CC) and coupled congestion control (Coupled CC), cannot achieve both bottleneck friendliness and throughput maximization for both of the MPTCP subflow bottleneck sharing scenarios, shared bottleneck (SB) scenario and non-shared bottleneck (NSB) scenario, leading to performance degradation in practice. In this work, we seek to enable efficient MPTCP congestion control, by alternating between Uncoupled CC algorithms and Coupled CC algorithms via smartly detecting whether the two MPTCP subflows share the same bottleneck link. We propose SmartSBD, the first learning-based data-driven approach for shared bottleneck detection, which is accurate, adaptable, and easy-to-deploy. SmartSBD is based on the key insight that the properties of subflows that share the same bottleneck often have similar trends of variation or similar values. In the training phase, SmartSBD collects system logs when MPTCP is running in real-world heterogeneous networks, extracts features, and trains a binary classifier. In the runtime phase, SmartSBD makes periodic predictions on the bottleneck sharing condition of live MPTCP subflows, and uses the prediction results to alternate between Coupled CC and Uncoupled CC. Our evaluations demonstrate that SmartSBD outperforms existing approaches.

A system-level multi-field coupling algorithm for regenerative cooling thrust chamber of a LOX/methane rocket engine

A systematic and hierarchical multi-physics coupling simulation method is proposed to model the combustion, combustion-gas transonic flow, coolant transcritical flow, and transient heat transfer phenomena inside the regenerative cooling thrust chamber subsystem of a LOX/methane rocket engine. By combining this algorithm with a self-developed platform, two distributed parameter modules are developed. Based on the ground test conditions of a LOX/methane engine, a verification case is established, and transient simulation studies are conducted. Comparisons with steady-state test data show that the calculated errors for coolant temperature rise and pressure drop are not higher than 4%. The simulation results reveal the locations where the transition from liquid to supercritical state occurs within the cooling jacket and provide three peril points of wall temperature on the thrust chamber. This study comprehensively reveals the occurrence of transcritical transient processes inside the cooling channels during the regenerative cooling process, laying the foundation for future entire system simulation.

Mechanic–electric–circuit coupling analysis of BAW filter based on FDTD method

AbstractIn this paper, mechanic–electric–circuit coupling algorithm based on the finite‐difference time‐domain (FDTD) method is proposed to analyze a one‐order microwave bulk acoustic wave (BAW) filter. FDTD method is used to solve the coupled mechanic–electric–circuit system equations to obtain the voltage and current at port position of the BAW filter in the time domain. Then S parameters of the BAW filter in the frequency domain are calculated using the Fourier transform. In our work, a one‐order BAW filter consists of two film bulk acoustic resonators (FBARs) by means of series and parallel. These two FBARs in the BAW filter are coupled together through an equivalent electrical connection. Similarly, multiphysical mechanic–electric–circuit analysis of the BAW filter is implemented in the commercial software COMSOL, which is realized by the time‐domain finite element method. The accuracy of the proposed method is verified by comparison with simulation results in COMSOL. In addition, the computational time and memory of the proposed method have obvious advantages over those of COMSOL.

Modelling the post‐buckling behaviour of steel sheets under induction heating

AbstractInduction heating has many engineering applications. To accurately describe the induction heating process of thin steel sheets one needs to account for their mechanical deformation. This might strongly affect the magnetic configuration since thin sheets are prone to thermal buckling, leading to large supercritical deformations. We suggest a modelling strategy combining a computationally highly efficient structural mechanical shell description for the thin sheet with a standard continuum model for eddy current and thermal problems through an iterative coupling algorithm. All benchmark problems are solved numerically using the finite element method.

Multi-constraint spatial coupling for the body joint quadruped robot and the CPG control method on rough terrain

Quadruped robots have frequently appeared in various situations, including wilderness rescue, planetary exploration, and nuclear power facility maintenance. The quadruped robot with an active body joint has better environmental adaptability than one without body joints. However, it is difficult to guarantee the stability of the body joint quadruped robot when walking on rough terrain. Given the above issues, this paper proposed a gait control method for the body joint quadruped robot based on multi-constraint spatial coupling (MCSC) algorithm. The body workspace of the robot is divided into three subspaces, which are solved for different gaits, and then coupled to obtain the stable workspace of the body. A multi-layer central pattern generator model based on the Hopf oscillator is built to realize the generation and switching of walk and trot gaits. Then, combined with the MCSC area of the body, the reflex adjustment strategy on different terrains is established to adjust the body’s posture in real time and realize the robot’s stable locomotion. Finally, the robot prototype is developed to verify the effectiveness of the control method. The simulation and experiment results show that the proposed method can reduce the offset of the swing legs and the fluctuation of the body attitude angle. Furthermore, the quadruped robot is ensured to maintain stability by dynamically modifying its body posture. The relevant result can offer a helpful reference for the control of quadruped robots in complex environments.

The parameter inversion in coupled geomechanics and flow simulations using Bayesian inference

In many situations, uncertainty about the mechanical properties of surrounding soils due to the lack of data and spatial variations requires tools that involve the study of parameters by means of random variables or random functions. Usually only a few measurements of parameters, such as permeability or porosity, are available to build a model, and some measurements of the geomechanical behavior, such as displacements, stresses, and strains are needed to check/calibrate the model. In order to introduce this type of modeling in geomechanical analysis, taking into account the random nature of soil parameters, Bayesian inference techniques are implemented in highly heterogeneous porous media. Within the framework of a coupling algorithm, these are incorporated into the inverse poroelasticity problem, with porosity, permeability and Young modulus treated as stationary random fields obtained by the moving average (MA) method. To this end, the Metropolis–Hasting (MH) algorithm was chosen to seek the geomechanical parameters that yield the lowest misfit. Numerical simulations related to injection problems and fluid withdrawal in a 3D domain are performed to compare the performance of this methodology. We conclude with some remarks about numerical experiments.

A Tight Coupling Algorithm for Strapdown Inertial Navigation System (SINS)/Global Positioning System (GPS) Adaptive Integrated Navigation Based on Variational Bayesian

Multi-source nonlinear noise exists in the process of multi-source navigation information fusion in long-endurance positioning systems in complex environments. In such engineering applications, the classical Kalman filter (KF) and the extended Kalman filter (EKF) have the phenomena of noise instability and parameter drift, which lead to the divergence of filtering results and reductions in accuracy over long periods of time. Aiming at the above problems, this paper proposes a fusion algorithm of the variational Bayesian (VB) and the cubature Kalman filter (CKF). Firstly, the system is modeled through nonlinear filtering, and the CKF error equation is established by taking the position difference and velocity difference between SINS and GPS as observation variables. Then, to address the problem of poor self-adaptation of the CKF algorithm, the variational Bayesian adaptive estimation method is introduced into the CKF algorithm, and a measurement noise variance estimation model is introduced to the process of time and measurement updates of the CKF algorithm to finally obtain the adaptive VB–CKF algorithm. The simulation results from the experimental platform show that the proposed fusion algorithm improves the combined SINS/GPS system by about 30% in terms of attitude angle accuracy and reduces speed and position estimation errors (RMSE) by about 45%. At the same time, comprehensive experiments on multiple types of sites show that compared with the CKF algorithm, the VB–CKF algorithm improves the positioning accuracy by 10% when the GPS signal is stable and improves the accuracy by about 38% when the GPS measurement noise changes dramatically in complex terrain, which effectively suppresses the accuracy divergence of the CKF algorithm and has high value for engineering applications.

Three-dimensional thermal-hydraulics/neutronics coupling analysis on the full-scale module of helium-cooled tritium-breeding blanket

Blanket is of vital importance for engineering application of the fusion reactor. Nuclear heat deposition in materials is the main heat source in blanket structure. In this paper, the three-dimensional method for thermal-hydraulics/neutronics coupling analysis is developed and applied for the full-scale module of the helium-cooled ceramic breeder tritium breeding blanket (HCCB TBB) designed for China Fusion Engineering Test Reactor (CFETR). The explicit coupling scheme is used to support data transfer for coupling analysis based on cell-to-cell mapping method. The coupling algorithm is realized by the user-defined function compiled in Fluent. The three-dimensional model is established, and then the coupling analysis is performed using the paralleled Coupling Analysis of Thermal-hydraulics and Neutronics Interface Code (CATNIC). The results reveal the relatively small influence of the coupling analysis compared to the traditional method using the radial fitting function of internal heat source. However, the coupling analysis method is quite important considering the nonuniform distribution of the neutron wall loading (NWL) along the poloidal direction. Finally, the structure optimization of the blanket is carried out using the coupling method to satisfy the thermal requirement of all materials. The nonlinear effect between thermal-hydraulics and neutronics is found during the blanket structure optimization, and the tritium production performance is slightly reduced after optimization. Such an adverse effect should be thoroughly evaluated in the future work.